The battlefront in Minnesota's fight against zebra mussels is spreading, now to the Iron Range, state conservation officials said Tuesday.

The invasive species has been found in a lake in a dormant mine pit near Gilbert -- the first time zebra mussels have been found in a mine pit and the farthest north they have been detected, according to the Minnesota Department of Natural Resources (DNR).

"It's another reminder that aquatic invasive species can travel great distances and don't have to be in a nearby lake or river to be a threat," said Rich Rezanka, a DNR invasive species specialist.

In this instance, adult zebra mussels were found in abundance about 250 yards south of the pit's boat access.

Most of the zebra mussels were large and none were less than 1 centimeter long.

The DNR reminded boaters who use the pit to be "extra thorough when decontaminating their boats, trailers, anchors and other equipment when leaving the infested lake."

Once the pit is officially designated as infested, it will come under restrictions on harvesting bait and transporting water.

Zebra mussels are considered a threat to Minnesota rivers and lakes because they multiply rapidly and attach themselves to native mussels, killing them and altering the ecology of food chains. Their hard shells also cut swimmers' feet and fishing lines and inundate docks.

For more information about aquatic invasive species, how to inspect water equipment and a current infested-waters list, visit www.mndnr.gov/ais.